The present invention relates to a method for drying of a protein-containing liquid, such as milk and milk-derived liquids for the manufacture of a powdery product.
Furthermore, the present invention relates to a system for drying a protein-containing liquid, such as milk and milk derived liquids, which due to heat sensitivity or formation of sticky or hygroscopic substances may be difficult to convert into a powder of high quality, such as a free-flowing, non-caking powdery product.
Yet furthermore, the present invention relates to a system for drying of milk and milk derived liquids in a process which is more energy efficient than the prior processes implemented by industry and at the same time provides an apparatus requiring lesser building volume than the previous apparatuses.
Milk powders are defined as follows:
Dehydrated products based on non-fat milk solids and milk fat, that is natural milk in which the fat content may be standardised by centrifugation or addition of cream to achieve the fat content required in the final product, between 0.5 and 30%, expressed on total solids.
Further the protein content of the milk may be standardised by means of addition of lactose or permeate in case the protein content in the milk supply is too high. These products are termed skim milk and whole milk powders, defined as milk powder with max 1% fat and 26% fat respectively. Fat filled milk powders are based on skim milk and vegetable or animal fat with a fat content of 10-80%.
Further, the milk powders may contain functional additives, such as emulsifiers stabilisers and flavouring and colouring agents.
Milk powders are used for various purposes such as ingredients in human and animal consumption.
In prior art several processes are known for manufacture of free-flowing, non-caking powdery milk products. In these known state-of-the-art processes milk is initially concentrated as much as possible, such as in a multiple effect falling film tubular evaporator. Thereby a concentration up to approx. 50% total solids (TS) is obtained.
This liquid product with approx. 50% total solids may then be spray and/or fluid bed dried and cooled in a fluid bed. (Masters, Spray Drying Handbook, 4 ed. 1985, Chapter 15.1, p. 575ff)
The mentioned prior art process is widely used in industry. It has, however several drawbacks.
First, the energy efficient multiple effect evaporation process can only be used to concentrate the whey to approx. 50% TS while the rest of the water removal requires a less energy-efficient air dryer. The limit of approx. 50% TS in prior art evaporators is set by the viscosity of the milk concentrate. Attempts to produce concentrates with higher total solids lead to un-pumpable products and formation of deposits which may promote growth of bacteria.
Therefore, since long the milk powder industry has an unfulfilled demand for a process for drying of protein-containing, such as milk and milk derived liquids for the manufacture of a powdery product substantially free-flowing, non-caking, and which process is more energy efficient than the prior art processes implemented by industry and at the same time provides an apparatus requiring lesser building volume than the previous apparatuses.
Accordingly, the present invention relates to a method and a system for producing a powdery product from a protein-containing liquid having a dry solid content comprising the steps of
providing a first feeding stream of the protein-containing liquid,
providing a second feeding stream having a higher content of dry solids than said first feeding stream,
mixing said first feeding stream and said second feeding stream obtaining a main stream,
heating the main stream in a heater,
transferring the heated main stream to a separator,
flash separating volatile components from said heated main stream obtaining a main stream protein-containing concentrate, and
subjecting at least a part of the main stream protein-containing concentrate to a drying step obtaining a powdery product.
By the term xe2x80x9cpowdery productxe2x80x9d is meant a product normally considered as powder, i.e. having a particle size corresponding to powder, such as preferably above 0.1 xcexcm and preferably below 2 mm, the particle size being measured as the approximate diameter of the particle.
Also the invention relates to a system for drying protein-containing liquids in a process which is more energy efficient than prior processes in that:
the amount of water to be evaporated in the drying step is significantly reduced, requiring smaller drying equipment, less air and less energy,
the total thermal degradation of particles is strongly reduced
a powdery product having higher xe2x80x9cbulk densityxe2x80x9d is obtainable